How Do You Calculate the Normalized Frequency for a Multimode Fiber?

[Bananen]

Hi,

I'm having trouble calculating the normalized frequency for a multimode fiber. Here's the formula:

V=(2π/λ)⋅a⋅√(n1²-n2²)

where λ=900 nm, a=200μm, n1=1.460, n2=1.455

Here's how I plug in the numbers:

V=(2π/(900*10^-9))⋅(200*10^-6)⋅√(1.460²-1.455²)=167This is an easy calculation I know that, but I get the wrong answer. It's supposed to be 84 but I get 167 which is obviously far away from the real answer. I don't understand what I do wrong?

 

[Metmann]

Well, the answer is 168.57... , so either the formula, the numbers or the supposed result are wrong. Since 84=168/2, it should be a matter of a factor of 2.

 

[pixel]

On my first attempt at calculating V I also get what you did. So that leads me to ask how you know it's supposed to be 84.

 

[Bananen]

Thank you, yes something must be wrong. It's very strange! But thank you for your answer.

 

[Bananen]

Pixel: I'm doing old exams in preparation for my own so I calculate exam problems and checking my answers by looking at the solutions. They don't write the numbers out just the formula and then the answer so it's not very helpful